1. Field of the Invention
This invention relates to an apparatus and method for radiographic diagnosis of, for example, circulatory cases, and more particularly to an apparatus and method for radiographic diagnosis used to introduce a catheter to the target portion of the subject.
2. Description of the Related Art
In a radiographic diagnosis, particularly that of circulatory cases, operations such as PTA (blood vessel formation techniques using a catheter) are performed, the operator inserts a catheter into a blood vessel and moves the catheter along inside the blood vessel to the target portion moves it to the target portion by watching the X-ray image on the TV monitor. It is difficult, however, to decide the way in which the catheter should advance, since no blood vessel is represented on the X-ray image.
To overcome this problem, in a known method, so-called road mapping, a blood vessel contrast medium is injected at one end of the catheter, and then the catheter is advanced, while the motion of the catheter inside the blood vessel is being watched. The road mapping has two methods. One method is a method of displaying both the blood vessel image obtained by being pre injected blood vessel contrast medium thereto and an image in parallel, and watching both of them. Another method is a method of obtaining a contrast blood vessel image by subtracting an image from a blood vessel contrast image obtained by pre-injecting a blood vessel contrast medium thereto, and displaying the direction of advancing the catheter by superimposing the blood vessel contrast image on X-ray image. The latter method is called as superimpose method.
An example of the superimpose method will be explained, referring to FIG. 1.
When a blood vessel contrast medium is injected through the catheter into a blood vessel, the blood vessel in which the catheter should move appears on the screen. With this operation, a contrast image 110 which contains an image 102 corresponding to a bone portion (hereinafter, referred to as a bone portion image data 102) and an image 112 corresponding to a blood vessel (hereinafter, referred to as the blood vessel image data 112) is obtained. A mask image 100 containing the bone portion image data 102 before injection of the blood vessel contrast medium is formed before the formation of the contrast image 110. After the mask image 100 is subtracted from the contrast image 110 at a subtracter 43, the background (including the bone portion image data 102 and muscle portion not shown here) is erased, creating the blood vessel image 120 consisting only of the blood vessel image 112. The blood vessel image 112 is multiplied by a given value of 1/a for brightness control.
An adder 150 adds the multiplication result, bone portion image data 120, and X-ray image 140 containing the image 142 corresponding to the catheter (hereinafter, referred to as the catheter image data 142) to superimpose each other. This addition produces a road map image 160 containing the bone portion data 102, blood vessel image data 112, and catheter image data 142.
With this road map image 160, the operator is able to easily move the catheter in the desired direction according to the blood vessel image data 112 of the map image, facilitating the maneuvering of the catheter.
Another method is to allow easy manipulation of the catheter by using a high-speed switch (not shown) to alternate between the process of displaying a blood vessel image data and the process of displaying the X-ray image containing the catheter image data to pretend to be superimposed thereof.
The superimpose method has the following problem.
Because the blood vessel image 120 is directly superimposed on the X-ray image 140, it is difficult to distinguish the catheter image 142 from the blood vessel image 120 at the overlapping portion. Since the direction of the catheter tip is very important in operations such as division of a blood vessel, a clear distinction between them is necessary. Once the blood vessel image data 112 has overlapped the catheter image data 142, it is more difficult to identify the catheter. In addition to this problem, it is less easy to watch the blood vessels and the catheter at a portion overlapping the bone image 102 and others.
Related literatures to the present invention are U.S. Pat. Nos. 4,204,225 and 4,878,115. In the former literature, a method for obtaining blood vessel image data is described, and in the latter literature, one method of superimpose method is described.
Further, another related art for observing only a blood vessel image easily by obtaining a peak hold thereof is disclosed in Japanese Unexamined Patent Application No. 1-178241. With this art, however, since a blood vessel image is displayed by only superimposing a catheter image thereon, it has a similar problem to above related art.